Amiloride binding protein (ABP1), also known as amine oxidase copper domain-containing protein 1 (AOC1), is an approximately 110 kDa member of the copper-containing amine oxidase family. ABP1 is a glycosylated enzyme that forms disulfide-linked homodimers. It is stored in cytoplasmic granules of epithelial cells in the kidney, placenta, uterus, lung, and intestine, and its extracellular release can be induced by heparin. ABP1 exhibits a substrate preference for histamine and putrescine, generating hydrogen peroxide and ammonia in an oxidative deamination reaction. ABP1 activity plays an important role in the catabolism of histamine and other bioactive polyamines. The activity of recombinant human ABP1 was measured by its ability to produce hydrogen peroxide during the oxidation of histamine. The reaction was performed in 50 mM HEPES, pH 7.5 (assay buffer), initiated by addition 50 μL of various concentrations of ABP1 (diluted by assay buffer) to 50 μl substrate mixture of 10 uM histamine, 2 units/mL HRP and 100 μM AUR. Read at excitation and emission wavelengths of 544 nm and 590 nm (top read), respectively in kinetic mode for 5 minutes.